Waterboard fin



FIG. 1 is a rear perspective view of a waterboard fin showing my new design, the broken line being for illustrative purposes only and forming no part of the claimed design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a bottom plan view thereof; and

FIG. 6 is a right side elevational view thereof, the left side elevational view thereof being a mirror image of that shown. 

The ornamental design for a waterboard fin, as shown and described. 